Now that's what I call holiday pay...

One department store's workers have their own private island, says Robert Nurden

Wayne from furniture ate his chicken fricassee, sipped his mineral water and looked out at the lawn where two peacocks were strutting their stuff. Beyond the sea wall a Brittany ferry loomed into view, towering over the little beach that was getting submerged beneath its wash. As it slid past, its passengers leant over the handrails peering into the private world of Brownsea Castle.

But the departmental manager of the Milton Keynes branch of John Lewis had seen it all before: it was the seventh visit he'd made with his family. Even in his faded holiday jeans and striped T-shirt he looked the loyal employee, the kind that the retail store with a heart spends thousands of pounds on retaining.

This ancient castle, on an island at the mouth of Poole Harbour, is one of four homes that John Lewis rents out to its 59,000 partners. But why, I wondered, would anyone want to go on holiday with work colleagues?

"It's four-star treatment at two-star prices," said Paula, Wayne's wife and a former JLP partner. "We don't actually come with workmates but over the years we've got to know the regulars. You don't have to spend all the time with them. It's the old-fashioned family values we like."

As well as the castle itself, with its 30 guest bedrooms, John Lewis leases 17 acres of land from the National Trust, owner of Brownsea Island, one a half miles by half a mile.

The notices have a whiff of the paternalistic about them. "Please ensure that children do not run around in the dining room during mealtimes. It is dangerous as the waitresses are serving hot food." The dress code harks back to the 1950s: "Smart dress is required for dinner - but guests are very welcome, of course, to dress more formally if they wish." And this from the handbook: "Guests are requested not to feed the peacocks in the castle grounds, especially on the terrace during afternoon tea." Standards, so vital.

But even the best behaved retailers need to let their hair down; quiz nights, jazz concerts, antique roadshows, nature talks, even the occasional bad-taste party, fit the bill.

"I don't like the look of them," said John D'Arcy, the castle manager, as two lads surreptitiously tiptoed down the main stairs. "I don't think they're anything to do with us." As they headed for the quayside, he beetled down the path after them and before they had a chance to board the boat lectured them about staying off private land.

Taking our cue from the recalcitrant youths, we slipped through the gate to explore the island. The landscape must be one of the most varied anywhere in such a confined area: muddy shoreline and brackish lagoon managed by the Dorset Wildlife Trust and home to birds such as egrets, terns, curlews, sandpipers, greenshanks, ruffs and plovers. Inland, there are freshwater lakes, open grassland, heath tracts, pinewoods and broadleaf woodlands. There's even a hillock that looks out over Poole Harbour and, on a clear day, you can see the Needles on the Isle of Wight.

At the northern end is a plinth commemorating Baden-Powell's first scout camp in 1907. The eagle-eyed can make out the ruins of Maryland, the village built for workers at the doomed china clay works set up by one Colonel William Waugh, whose dreamed-of fortune never came to fruition.

The Japanese Sika deer that roam the island are elegant but something of a pest: they gnaw the bark of saplings and prevent hundreds of trees from reaching their full growth. But they, too, have an interesting story: they were forced off the island by a devastating fire in 1934, swimming the one and a quarter miles to the safety of the mainland. Ever since, herds have been making the reverse trip.

Much of the credit for Brownsea's virgin landscape must go to the eccentric Mrs Mary Bonham-Christie who owned it from 1927 until her death in 1961. She banned visitors and allowed farm animals to roam wild. When the National Trust took over it introduced a management programme that allowed species such as pine, chestnut, oak and poplar to flourish again.

There's even a village green complete with ducks, hens, geese, peacocks, a farm and a church lit solely by candelabra. As we sat on a bench in the twilight drinking in the ancient rustic scene, we could almost have been figures in a Claude-Lorraine landscape. It is here that, every August, an open-air opera is staged.

After dinner that evening John led us up a narrow stairway to the roof of the castle. Lights twinkled in an arc to Swanage, beaming an orange glow into the fading sky.

In the lounge a palm-court piano was playing, the regular Sunday night recital from a music teacher on the mainland. The performance provided soothing background tinkling for the relaxing retailers, who were slumped in chairs half-reading the papers or just snoozing: clearly, John Lewis staff have never knowingly under-holidayed.

Robert Nurden was a guest of the John Lewis Partnership. Access to Brownsea Island for National Trust visitors is by boat from Sandbanks (£3.50) or Poole Quay, Bournemouth (£5). National Trust Brownsea Island (01202 707744; www.national trust.org.uk/brownsea).